Remote control 4: the emitter

b – connect one led between left and right channel (don’t care GROUND)

c – connect the other led between left and right channel, but the opposite direction

Your emitter should look like this:

Please note the opposite orientation of the two leds!

You should connect them to your headphone cable this way:

Ok, your emitter is ready.

Unfortunately, as it is it will be very weak, and it will have just a few centimeters range! To get a suitable range you need a suitable power; and to get more power than the phone can provide, you need an amplifier.

An amplifier is an electronic circuit which uses an external power source to add some power to a weak electric signal; you can build a simple one using just a few components: 5 resistors and 1 transistor:

The resistors are the component which have a “xxx kOhms” label; the transistor (here, actually, a “double transistor”, properly a “darlington”) is in the circle.

The external power here comes from a 9V battery (bottom left in the picture) .

Let’s divide the circuit in parts to better understand it.

We have a voltage divider: this set of components divides the voltage in parts, depending on how it is built, according to formula:
Vout = Vin * R2/(R1+R2)
If R1 = R2, Vin is exactly splint in 2 equal parts: Vout = Vin / 2
This means that in our circuit the voltage in Vout will be 4.5V if we use a 9V battery.
Why do we need this voltage divider? Because the input signal coming from phone to our amplifier will have positive and negative values (its carrier is a sinusoid), so if the base of the transistor was biased at 9V, transistor wouldn’t be able to amplify positive parts of the wave, being it at higher voltage than the battery; if it was biased at 0V, negative parts of the input wave would be lost; we need “the right in the middle value”: 4.5V

Now we can add the transistor, which will get Vout as input to its base:

In case the current/signal coming from the phone was too high, we need a limiting resistor on the input; I don’t know how actually high can the phone output voltage be, anyway the current that will flow trhough transistor will be Iin = Vphone/R3. This current will just activate and drive the transistor, it does not flow through the speaker:

The current which flows in the speaker is determined by the battery voltage, not by the phone voltage; the power which the transistor must handle due to surrounding components is given by P = V^2 / Rs, where Rs is the internal resistance of the speaker, which we do not know:
but we know from datasheet that the MPSW45A cannot tolerate more than 1W (Pd value); to get Pd<=1 we must have V^2/Rtot <=1 ,i.e 81<= Rtot , where Rtot is the total resistance given by sum of speaker resistor and additional R4: we get that it must be Rtot = Rs + R4 >=81 ohm , and Iout would be Iout = V/Rtot <= 9/81 = <=111 mA: for this current flowing through the transistor we get around the maximum amplification, as we can see from datasheet:

In “phone world”, 5V is a most common voltage (USB charger voltage); what does it happen by applying 5V to this circuit rather than 9V?

The original site the schematic comes from does not explore this case… but I assume that we would get:

Rtot >=V^2 –> Rtot >=25

Vbase = 2.5V

P = 25/Rtot

25/81= 0.3 = 1/3

This means that by sure the transistor won’t get damaged, and it also probably means that we’ll get an output power wich is 1/3 of what we get using 5V, assuming we use same R4. To get same power of the 9V-powered amplifier, I think we’d need a total resistance Rtot >= 25 Ohm; R4 value is given by: R4 = Rtot – Rs = 25-Rs.

OH MY GOD! You are a GENIUS! I read dozens of tutorials to create a ir transmitter but this is the one that worked and i finally got access to my TV system menu for just 6€ in materials from a chinese store! Thank you very much for this awesome tutorial!

I couldn’t get this to work. I built the IR receiver and when I connected ground and one channel to the one LED, I wouldn’t get any signal but if I connected ground to both receiver LED’s and and one channel to each of the other pins of the LED, i captured something. After completing the transmitter and editing the waveforms and such, and I played the sound, nothing happened. =(

John, I didn’t clearly understand what kind of connections you did, can you explain it better?

Anyway, once you record the sound, you cant just play it to drive your TV set: your remote control signal is “filtered” by the IR receiver, i.e. it’s actually CHANGED, so you have to rebuild it to obtain a suitable signal.

I got this far fine in the guide, but after building the emitter and playing the wavelength back, I couldn’t get the emitter LEDs to light up (watching them through a digital camera to see the IR part of the spectrum).

I’ve checked all my connections 10 times and tried with 2 different wires, and made sure the LEDs are working. Still no light. Any idea where to go next?

I need more details to be able to help you.
Which phone are you using?
Did you try playing a music file, just to see if actually LEDs light up? (maybe files you’re playing are too short to be human-visibile).
How did you connect leds to phone? (can you send me any photo?)

I’m having the same problem. The I connected the LEDs(tried both Infrared Phototransistor and Infrared Emitter from radioshack) exactly as shown in with the ground from the headphone jack not connected to anything and the left and right connected to both LEDs in parallel with polarities reversed. I tried using my iphone to play back the sound and tried just playing music and the LEDs did not light up(looking through a digital camera). I checked both LEDs separately and they light up but when I put them in the configuration described, they don’t light up. Any ideas? Thanks in advance

Ok so let me give a more precise description. I just wanted to try this and turn on and turn of my tv through this infrarred device (through the audio jacks). so i went to radio shack and bought all my stuff. i bought a Stereo Audio Cable (3.5mm) and some aligator clips. one receiver and one transmitter. So i am not sure if the 3.5mm audio cable is the same as the headphones. this cable is actually called 1/8″ (3.5mm) Stereo Male to 1/8″ (3.5mm) Stereo male. and so i cut it apart. there were three cables. one the ground. one red and one black. so i connected the ground and the red to the LED IR receiver. (if i connected the black i would get weird looking waves) (it also depended on what side i plugged the ground to on the receiver). the only difference is that my waves were downard going. they were exactly the same as the ones in this tutorial except always facing downards (the squares) anyways i proceeded on converting the waves and got them ready. the hard part came assembling the transmitter. i noticed you have two of them. well i have one LED transmitter and i dont think i need two since i am not using headphone cable. but for me it seems not to work. i even cut my new iphone earphones just to try it and i cant even get signal from those headphones for recording. any help? thanks!

Are you using a phone or a PC to play the tone you created ? using cellphones is quite harder than PC.
You usually need two leds because the signal has 38000 Hz frequency against 20000 Hz maximum frequency of typical audio devices.
But you don’t have to connect the two leds just like if they were earpieces: you have to disreagrd ground, and to connect both leds to left/right channels, one the opposite way of the other: this results in single waves of two leds being “summed up”. So, each led has to emit a 19000 Hz wave, with opposite phase one w.r.t. the other.

Anyway, it looks like modern PC soundcards have a very high bandwidth: my EEEPC 701g is capable of properly sample the 38000 Hz signal carrier, thus I don’t see just a square wave, but a series of “carrier bursts” and silence, just when I usually saw “high” and “low” signal using my old PC.
I didn’t yet test if transmitting the signal as it was acquired, using one single led, is enough to control the TV set.

I am using a pc to do this. Phone would be the second step. Is there anyway you can send me a screenshot of how your waves look? So even with pc i need two leds? Hmm. It depends how i connect the receiver. If its to the red cable and ground its square waves if its to the black cable and ground is thousands of lines and waves. but since the tutorial says they should be squared i thought i need to use the squared. you think that the 3.5mm cable for this experiment is good or do i really need headphone cable? I just want to build a smal IR blaster and have it about the size of 1 or 2 cm. but i dont want it to have 3 leds: receiver, transmitter, transmitter. is that not to much? i am getting little lost. i just want to turn on and off my tv. could it be because i am recording this frequency from a universal remote instead of the tv’s remote?

Let’s clarify:
you need ONE led connectd to ONE cable to SAMPLE the remote (‘cause you already know the frequency, you just need durations), and TWO leds connected to ANOTHER cable to transmit an ARTIFICIAL signal you created starting from a 38000 Hz tone in which you deleted some parts to match durations to the ones of the sampled signal.

Ok i get it. so i need two leds. I will go and get it. Too bad i cant construct the IR blaster using two leds and the same cable. i’ll have to figure that out. so you think that one led is not enough? is there any program that can do all the music (wave frequency) converting for me? instead of using audacity? cause in the end i want to make a simple small device for my phone jack. instead of using tons of cables and two leds. damn… well i need to go find a remote 🙂
thanks for the new post.

You have to export as WAV from audacity just ONE of the multiple occurrences of the signal (your remote keeps repeating same signal as long as you keep key pressed), then pass it to RAW2LIRC, which creates an intermediate LIRC file, and then pass this file to LIRC2LEDREM: this SHOULD result in a batch file which, once ran, will create the final WAV file you need! (phew!!).
Yes, quite tricky…

Do you know of any program that would do all the audio / ir frequency wave converting? Is there also a list on the internet of all the frequencies for all tvs and dvds so you dont have to record it? Like a file or something…

yeah quiet a lot cause today i had to buy a remote and take it out…cause everything was closed… yeah how do i send you the wav file? email? or? maybe i am doing something wrong with the assembling. but i doubt that… THank you!

Hello jumpjack, i finally got the receiver and Audicy to capture my remote control signal. I’ve build up the transmitter as shown in the figures and when i press Play in Audicy nothing happens. I’ve already rebuild the signal creating a tone and silcencing the unneeded parts. I’ve also joined both mono track (one of them inverted) getting a Stereo Track of 44100hz 32bit. Most probably there is no problem with the signal, however, as mentioned above, the leds of the transmitter do not light up. What can be the problem?, i can see in my headphone cable that in each channel, the ground cable touches the channel, can this be affecting the transmission?.
Thanks in advance!

Of course the ground wire must NOT touch the signal wire! But probably your wires are actually insulated, although you can’t see it: in very thin cables the insulation is just kind of a “painting” on the copper.

Can you send me a picture of how you build your emitter? jumpjack at libero dot it

Hello jumpjack, I have a little question. My IR emitter LED working voltage is 3V. But I test the voltage between the left channel and the right channel, it just output 5mv. And I use the dc to see the LED. It do not work. Did I make something mistake?
By the way, when I record the signal of left channel and right channel. I got the same signal, it didn’t look like what you say two different singal form( triangles and rectangles). Could you give some suggestions to help me.

Hi all, This is a great project and finally my hope of diy remote on my iphone is possible. I ran into the same problems. I made the emitter as instructed but when I put a digital camera up to the emitter I see nothing, I do however see the IR from the remote. I tried various contact configurations still nothing. I saw that many people had the same thing, but no solution. Any ideas from jumpjack on this problem.

Hi everyone,
I just wanted to mention that since I was making tests using the led of a spare remote control, I decided that I might as well try to plug directly the remote into the sound card, by replacing the ir emitter led by the jack cable. It made some good results for I then could visualize great signal in audacity, but I did not have the time to go further.

I followed this tutorial step by step and I got the two leds emitting by playing the waveform in Audacity but not strong enough to change my TV. I wonder if it could be because I connect the audio jack and the two leds with no audio wire, but some alligator clips.

I also have an USB-UIRT which I use to capture IR codes from some remotes and it allows me to emit some IR codes through its audio output. If I plug the audio jack with the two leds in UIRT’s audio output, I can manage my TV because the two leds light up much more strongly.

The problem can’t be related to the waveform because UIRT reacts with any IR signal (with the correct frecuency) and when I place the two leds opposite UIRT, it does nothing.

Any ideas of how could I do to the two leds emit more brightly (at least to keep on testing)?
Thanks in advance.

hey im having problems with this here i was wondering if anyone could give me some help. i got and android. i took an old remote for tv apart and got the ir. took the cable apart and i have wired it every way i can to get audacity to recieve something but i just dont see what i am doing wrong here. any trouble shooting would be helpful. thx in advance

The worst thing it could happens if you add a resistance is that LED will have not enough power to transmit. The worst thing that could happen if you do not add it is that soundcard get burnt (although I think they’re so low power and for so short time that it cannot happen).

Hi jumpjack, Inspired by your blog I started making DIY IR remote for phones…I made the emitter and there are many apps on the playstore to get your camera take photo through external IR module connected to the audio port of the phone….But the Emitter is bursting very weak signal (Seen through camera) and I am not able to get it to work…Any suggestions

PS: I am thinking of doing the sampling of tv remote controls using audacity after this small step succeeds.